Post e-filing, Turbotax says to "Mail These Forms to the Government" but won't say which forms it means.

After e-filing my federal and state returns, I received the following message on the screen in the program:

 

"Print and Mail These Forms to the Government. Even though you e-filed, you're still required to print and mail these forms"

 

However, TT did not specify what forms it meant. There was a link that said "explain this". But when I clicked the link, nothing happened. Just an error message popped up.  

 

Is this a glitch in the program, or must I file some other form? If so, which one?